Prewarm upcoming queue streams

frontend/app.js

@@ -623,8 +623,9 @@ const API = {
 // Pre-resolve streams for videos the user is likely to play next (server
 // /api/streams/warm). Each id is warmed at most once per 20 min per tab.
 const warmedAt = new Map();
+const knownServerCachedIds = new Set();
 function warmStreams(ids) {
-  if (!WEB || navigator.onLine === false) return;
+  if (!WEB || navigator.onLine === false || navigator.connection?.saveData) return;
   const now = Date.now();
   for (const id of ids) {
     if (!id || !/^[A-Za-z0-9_-]{11}$/.test(id) || cachedIds.has(id)) continue;
@@ -634,6 +635,14 @@ function warmStreams(ids) {
   }
 }
 
+function warmNextQueue() {
+  if (!window.PrewarmNext || queueIndex < 0) return;
+  warmStreams(window.PrewarmNext.candidates(queue, queueIndex, data.settings, 2, {
+    offline: cachedIds,
+    serverCached: knownServerCachedIds,
+  }));
+}
+
 // Resolve a native file path to a URL the WebView can load (Tauri asset
 // protocol). Returns null on shells without it.
 function toAssetUrl(path) {
@@ -2332,6 +2341,7 @@ const Player = {
       if (seq !== this._loadSeq) return; // a newer load took over meanwhile
       if (!res || !res.ok) throw new Error(res?.error || 'Could not load streams');
       current = res.data;
+      if (current.serverCached && current.meta?.id) knownServerCachedIds.add(current.meta.id);
       // Merge richer metadata we may already have from the list card.
       current.meta = { ...videoObj, ...current.meta };
 
@@ -3014,7 +3024,7 @@ function wirePlayerEvents() {
         perfMeasure('ytp:tap-to-play', 'ytp:tap');
         try { performance.clearMarks('ytp:tap'); } catch { /* ignore */ }
       }
-      if (Array.isArray(queue) && queueIndex >= 0) warmStreams(queue.slice(queueIndex + 1, queueIndex + 3).map((x) => x && x.id));
+      warmNextQueue();
       showSpinner(false);
       Player.clearBufferGrace();
       if (Player.secondary && !el.paused && Player.secondary.paused) {
@@ -8043,6 +8053,7 @@ function playFromList(list, index, source = '', { playFull = false } = {}) {
   unshuffledQueue = null;
   // Play-in-full keeps the list order — a service set plays as arranged.
   if (data.settings.shuffle && !playFull) applyShuffle();
+  warmNextQueue();
   Player.loadVideo(queue[queueIndex]);
   renderUpNext();
 }

frontend/index.html

@@ -693,6 +693,7 @@
     <script src="piano.js"></script>
     <script src="setlist-import.js"></script>
     <script src="car-mode.js"></script>
+    <script src="prewarm-next.js"></script>
     <script src="app.js"></script>
   </body>
 </html>

frontend/sw.js

@@ -124,6 +124,7 @@ const SHELL = [
   '/piano.js',
   '/setlist-import.js',
   '/car-mode.js',
+  '/prewarm-next.js',
   '/car-mode.css',
   '/lower-third.css',
   '/settings-sections.css',